Molding core grit

ABSTRACT

A FOUNDRY MOLD AND CORE ARE PREPARED USING COMMINUTED WET BOTTOM BOILER-SLAG AND A BINDER.

Dec. 12, 1972 I Ks 3,705,863

MOLDING CORE GRIT Filed 001'. 13, 1970 /v VEN TOR THOMAS 0. HICKS BY T TORNE Y5 United States Patent U.S. Cl. 260-22 TN 5 Claims ABSTRACT OF THE DISCLOSURE A foundry mold and core are prepared using comminuted wet bottom boiler slag and a binder.

The present invention is directed to the metal casting industry and is more specifically directed to the molds and cores utilized in the forming of castings. When referring to either or both of these, the term molding element will be used.

The metal casting industry is one that goes back a great many years. A variety of casting techniques have been utilized in the past, including the use of sand materials for molding elements. It is to this use of a sandlike material that the present invention is directed.

The requirements for such molding elements and the sands used therein include the following. The sand used should have high temperature capability, a low coeflicient of expansion with temperature, be bondable with a variety of materials, be nontoxic, have a low density, and be of low cost. In the actual molding elements, the sand-like material should provide good gas permeability through the structure to allow for escape of gases generated during the casting. After completion of the casting, the sandlike material used as the molding element should be readily removed from the casting.

The prior art has utilized a wide variety of sand-like materials, with the most common sands being of the silicon dioxide type. Silicon dioxide type sands are widely used, although for precision castings they possess certain undesired properties. One of the principal properties objected to is the high expansion coefficient of this material. The use of materials having high expansion coeflicients for the sand portion of molding elements results in a variety of problems to the casting industry. First, the high expansion of this material requires that the expansion coetficient be planned into the design of the mold in order that the finished product have the desired size. Another important drawback is the fact that, due to the high temperature coefiicient of expansion, the molding element tends to crack on being hit by the hot molten metal, giving rise to veining. That is, fine cracks appear in the core and mold which result in passage of some of the metal into the crack to leave veins of metallic material where none was desired, On the exterior portions of the casting, these veins require additional cost to remove, while in the interior of the casting such veins are sometimes impossible to reach.

In place of the silica-type sands, one may use sands having low thermal expansion coefiicients such as zircon sands or zirconia. These latter materials generally satisfy the above requirements, but have two major drawbacks. First, they are relatively expensive, and therefore increase the cost of the casting. Second, they are also of very high density. The high density is undesirable for the increased weight of the molding element in the finished form, which makes handling more difiicult. Also, the high density provides additional difficulties in the actual forming of the molding element and in removal of the zircon sand after casting. The high density makes more difficult the passage of the sand material into or out of the intricacies of the more complex molding elements.

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I have discovered that molding elements can be fabricated from a material that is readily available as a byproduct of the power generating industry. This by-prodnet is referred to in the art as wet bottom boiler slag. This material satisfies all of the criteria set forth above and is superior to the aforementioned zircon and zirconia materials in that it has a much lower cost and its density is about two-thirds that of zircon and one-half that of zirconia. It is available in a wide variety of particle sizes and readily bonds to form the molding elements using conventional bonding materials.

BRIEF DESCRIPTION OF THE DRAWING The sole figure is a cross-sectional view of a hydraulic valve body with a core and mold used in forming the valve in elevational and cross-sectional view, respectively.

Wet bottom boiler slag is a material that results from the use of coal in the manufacture of electric power. It has heretofore found use as a synthetic blast grit. It is available from H. B. Reed and Company, Inc. of Hammond, Ind., under the trademark of Black Beauty Blast Grit. The typical chemical composition of this material is as set forth below.

Percent SiO 42.66 FeO 23.05 CaO 6.41 TiO .95 A1 0 20.97 PC2013 MgO 1.11

While the above composition is shown as having a chemical composition including silica, it has been determined that this material does not include any free silica. As free silica is the cause of the disease referred to as silicosis, the absence of free silica is obviously an advantage over the silica sands used in the prior art.

The precise composition of the above material is not known with certainty. It is reasonable to assume that the composition is a variety of silicates of the various oxides enumerated. The color of the wet bottom boiler slag is a deep black. Its melting or softening temperature is in excess of 2200 F. The density is approximately 2.8. This compares to a density of 4.56 for zircon and 5.6 for zirconia.

I have found that using wet bottom boiler slag as the sand provides a very high yield of good castings, even when the castings have high precision requirements and are of very complex configuration. For example, referring to the sole figure, there is shown in cross sectional view a casting of a hydraulic valve with the mold body and core still in place. The mold body is shown in section, while the core is shown in elevational view. The casting 10 is shown still connected to the gates 11 used to introduce the molten metal into the cavity, The core is generally identified 12, while the external mold body is identified 13. The core and mold may be formed in accordance with the invention utilizing the common techniques utilized with other sand or grit materials. The advantages of use of the material in accordance with my invention include those heretofore enumerated. The yield of good castings using my invention was virtually percent.

The molding core grit of my invention is a material which results from the comminuting of the wet bottom boiler slag. It is segregated according to sizes utilizing sieves. Thus, by the control of the comminuting process, one can achieve particle sizes over an extremely wide range and thus obtain almost any size particles and distribution of sizes desired. In common with the practice commonly used in foundries, I have found that the particle sizes should lie within the range of U.S. standard sieve sizes from No. 16 through 270. This corresponds to a sieve having an opening from .0469 to .0021 inch. In actual practice, the particle sizes may vary within the entire range described and includes some fines which are smaller than 270. It is desirable that at least 80 percent of the particles be in the range of sieve sizes 16 to 50. The chart below is illustrative of the particle size distribution in percent of commercially available comminuted wet bottom boiler slag supplied by H. B. Reed and Company, Inc.

Percent US. sieve size 16 20 30 NOTE.Percentages in parentheses indicate total particles in and below sieve size shown.

As can be seen, the particle distribution within any commercially available grade varies over a considerable latitude. By a more extensive screening effort, one can limit the particle size to a narrower range, if desired. For best use, it is desirable that the amount of finely divided material be minimized to allow greater gas permeability of the completed core and mold.

All conventional binders used in the industry have proved usable with wet bottom boiler slag to produce molds and cores suitable for the casting industry. The materials that I have found to be operable include such diverse materials as synthetic resins based upon polyurethane and linseed oil, and the inorganic binders such as sodium silicate, which is cured by the use of carbon dioxide. Due to the sharp edges of the particles of wet bottom boiler slag in accordance with the invention, excellent bonds and high gas permeability result regardless of which type of a mold binder is utilized. The quantity of binder is variable over the normal limits of one to ten percent by weight, with the principal criteria being to use only so much binder as is necessary to secure the particles together with sufficient cohesiveness to withstand the handling and metal pouring. It is desirable to use from one to five percent by weight of the binder material, with ap proximately three percent being preferred. Examples of suitable organic binders are those described in US. Pats. 3,255,500, 3,409,579, 2,963,456, and 3,428,110. The first two of these patents teach binders that cure at room temerature.

I claim:

1. A cured foundry molding element consisting essentially of from 90 to 99% by weight comminuted wet bottom boiler slag having a density of about 2.8 and the balance a binder therefor.

2. A molding element in accordance with claim 1 wherein at least 80 percent of the slag particles are in the range of US. standard sieve sizes of 16 to 50.

3. A molding element in accordance with claim 1 wherein the binder is selected from the group consisting of inorganic and organic binders and comprises from one to five percent by weight of said element.

4. A molding element in accordance with claim 3 wherein the binder is an organic polymeric resin.

5. A molding element in accordance with claim 4 wherein the resin is a linseed oil-polyurethane-mixture.

curing at room temperature.

References Cited UNITED STATES PATENTS 2,870,110 1/1959 Cooper et al 26029.3 2,895,936 7/1959 Archer et al. 26037 3,255,500 6/1966 Engel et al. 164---43 2,487,207 11/1949 Adams 164-43 2,869,196 1/1959 Cooper et a1 164--43 2,963,456 12/1960 Betts et al. 26023.7 3,002,948 10/1961 Lawther et al 26038 3,567,667 3/1971 Rumbold 260l7.2

DONALD E. CZAJA, Primary Examiner R. W. GRIFFIN; Assistant Examiner US. Cl. X.R.

106-38.2, 38.9; 164-43; 260DIG. 40 

